Vibrationless pneumatic impact tool



June 5, 1956 s. ALTSCHULER 3 VIBRATIONLESS PNEUMATIC IMPACT TOOL FiledJan. 13, 1953 2 Sheets-Sheet l F q l Samuel Alzsafz u/er June 5, 1956 s.ALTSCHULER VIBRATIONLESS PNEUMATIC IMPACT TOOL 2 Sheets-Sheet 2 FiledJan. 13, 1953 United States Patent VIBRATIONLESS PNEUMATIC IMPACT rooLSamuel Altschuler, Chicago, llL, assignor to Armour Re search Foundationof Illinois Institute of Technology, Chicago, 111., a corporation ofIllinois Application January 13, 1953, Serial No. 330,971

11 Claims. (Cl. 121-25) The present invention relates to a substantiallyvibration-free, pneumatically operated tool, such as a sand tamper, rockdrill, demolition tool, pile driver or the like.

Among the major defects found in the prior art tools of the type abovementioned, all of which utilize a reciprocating motion, are the largevibrations and force reactions which are imposed upon the operator ofthe tool. These forces are transmitted to the operator through thecasing and handle, and seriously detract from the performance of thetool, both as to accuracy and as to the tiring effect upon the operator.

The nature and extent of the reactions in the prior art tools have beendependent to a large degree on the mass of the tool body, or pneumaticpiston cylinder, the mass of the piston and the rate of reciprocation.The effect of these factors in all of the tools of which I am aware, hasbeen a vibration that detracts materially from the operators efiiciency.

The present invention provides a substantially vibration-freepneumatically operated impact tool which overcomes the disadvantagesnormally associated with pneumatically operated reciprocating tools.Further, the tools constructed according to the present invention arerecoilless when operated in a substantially vertically downward positionand are subject to only a constant, non-vibrating, recoil force whenutilized in a horizontal or inverted position. This is generallyaccomplished by providing a system in which two masses move inopposition to each other in such a manner that the vectorial sum oftheir momenturns is substantially balanced. Since these masses are inmotion, kinetic energy can be abstracted from one or both of them to dothe work. A floating handle member is then associated with the tworeciprocating masses in a semi-isolated manner so that it retains themasses in their proper paths of motion without receiving any reactionforces from them.

An object of the present invention is, therefore, to provide a balancedsystem of reciprocating masses, which is supported and controlled byhandle means so that the system can be controlled in its direction ofapplication without imparting vibrations to the handle and hence, to theoperator.

Another object of the present invention is to provide a substantiallyvibration-free pneumatically operated tool.

Still another object of the present invention is to provide apneumatically operated tool which is recoilless when operated in thevertically downward position.

Yet another object of the present invention is to provide a constantrecoil, vibration-free reciprocating tool for use in a horizontal orinverted position.

Still another object of the present invention is to provide apneumatically operated tool including a reciprocating tool element, andan oppositely reciprocating coaxial piston, and a handle for supportingand guiding both the tool element and the piston while at the same timebeing carried by the tool element so that no shock or vibration isimparted to the handle.

Yet another object of the present invention is to proice vide a verysimple, lightweight reciprocating tool which is capable of greataccuracy of operation.

Still a further object of the present invention is the provision of amethod for applying a substantially constant recoil reaction force to areciprocating tool used in a horizontal position, without imparting atthe same time vibration to the handle operating means.

Still other and further objects will become apparent to those skilled inthe art from a consideration of the attached sheets of drawings, whichby way of preferred example only illustrate a tamping tool embodying theprinciples of the present invention.

On the drawings:

Figure 1 is a longitudinal sectional view, of the tamper of the presentinvention at the start of one cycle of opera-- tion Figure 2 is alongitudinal section similar to that in: Figure 1 and illustrating theposition of the parts afterits introduction of compressed air to causeopposite re-- ciprocation of the reciprocating masses;

Figure 3 is a cross-sectional view taken substantially along the lineIiIlII of Figure 1;

Figure 4 is a cross-sectional view taken substantially along the linelV-lV of Figure l; and

Figure 5 is a longitudinal elevation, in partial section,.

showing a modified form of the tamper of the present inventionincorporating a constant force applying recoill chamber.

As shown on the drawings:

As may clearly be seen from Figures 1 and 2, the' tamper illustrated inthe drawings includes a hollow handle or sleeve 1!) having annularflange portions 11 and 12 at the opposite ends thereof. The flangeportion 11 is suitably bored to provide an inlet port 13 for the introduction of compressed air or other expanding gas intothe assemblythrough a pipe fitting 14.

Inside the handle 10 and supported therein for sliding; movementrelative thereto is a tool assembly. This as-- sembly includes acylindrical sleeve 16 which is freely' slidable within the sleeve 10 inbearing contact with av pair of substantially frictionless bearingsurfaces 17 and 18 on the annular flanges 11 and 12.

In order to provide an annular air supply chamber substantially thelength of the handle, the handle 10 is recessed to provide an annularspace 21 surrounding the central portion of the sleeve 16 so that theonly points of contact in the sleeve 16 and the handle 11) are at thebearing surfaces 17 and 18.

A tool member 23 is fixedly secured to the sleeve 16 by means of weldingor other equivalent fastening processes at the mounting shank 21.

The opposite end of the sleeve 16 is closed by means of a closure plug24- having an annular flange surface 25 overlying the sleeve 16. Thisplug 24 is likewise secured to the sleeve 16 for movement therewith.

A porting tube 30 is supported on the same axis as the sleeve 16 and thehandle 16, with one of its ends secured within a recess 31 provided inthe tool shank 21 and its other end secured to the plug 24 in anair-tight manner. As is shown in Figure 2, the porting tube 30 issubstantially hollow except for a central plug portion 32 which provideswithin the porting tube 36 a pair of longitudinally disposed airpassages 33 and 34.

Mounted for reciprocation between the porting tube 30 and the innersurfaceof the sleeve 16 is a reactive mass or piston 35. A plurality ofair inlet ports 36 are laterally radially drilled in the piston 35 andserve as passageways for the introduction of air to an annular cavity 52between the piston 35 and the tube 30. An annular passage 39 is providedin the piston 35 in connection with the ports 36 and is adapted tocooperate with a plurality of peripherally located apertures 40 in thesleeve 16. Valve ports 42 and 44 are provided at the opposite ends ofthe passageway 33 for controlling the flow of air through thepassageway. A further valve port 54 is provided at the lower end of thepassageway 34, and the passageway 34 is vented to atmosphere at itsother end.

A reduced bearing portion 37 is provided at the cen tral portion of thepiston 35 to provide a bearing surface and also act as an air-tight sealin the valving construe tion.

In the position of the apparatus as shown in Figure 1, air introducedthrough the inlet port 13 of the handle can pass through theannularspace 2%, through the aperture 40 provided in the sleeve 16 andthence to the annular passageway 39. The air under pressure then flowsfrom the passage 39 through the ports 36 into the passage 52, throughthe ports 4-2 and the passageway 33 to the ports 44. The air then passesthrough the ports 44 to the space 45 between the piston 35 and the shank21. It is noted that with the parts 35 and 21 in the position shown inFigure 1, it is necessary to provide a slot 22 and an annular passageway28 to permit the air under pressure to be applied over a horizontalsurface of the member 35 to effect a lifting action.

The expansion of the compressed air in the chamber 45 forces the piston35 upwardly against a spring 49 and at the same time forces the tool 23with its attached tubes 16 and 3t) downwardly against the spring 49. Inorder to aid the spring 49 to arrest the movement of the piston 35, andthe plug 24 toward each other, the construction of the present inventionutilizes a trapped air chamber 53. This chamber is normally atatmospheric pressure, since it is vented at 54. It will be seen,however, from a comparison of Figures 1 and 2, that as the members 35and 24 near each other, the surface 37 closes off the vent between thespace 53 and passage 34. This traps air in chamber 53 and continuedmovement of the parts is resisted by the trapped air which acts as acushion.

After the compressed air has expanded to its maximum volume and inertiaforces have carried the parts 24 and 35 to their extreme positionsagainst the force of the spring 49 and the trapped air in chamber 53,the parts are in the position shown in Figure 2. In this position theexpanded air is vented to atmospheric pressure in the following manner:The piston 35 has now moved upwardly relative to the valve tube so thatthe ports 54 and 42 are in connection with each other by means of theannular passageway 52. The compressed air, which is still undersubstantially higher than atmospheric pressure, is thus vented from thechamber 45 through the ports 44, through the passageway 33, through theports 42 to the passageway 52 and thence through the passageway 54 andout through the vent passageway 34 to atmosphere. Reciprocation of theparts provides enough inertia effect so that the valve ports 54 will beopen to the passageway 52 long enough so that the fluid pressure in thechamber 45 will be reduced substantially to atmospheric pressure atwhich time the spring 49 and the trapped air in chamber 53 force themember downwardly and the tool 23 upwardly until the parts assume theposition shown in Figure l in readiness for the repetition of the cycle.

An important feature of the present invention is the adjustment of themass of the tool assembly which includes the sleeve 16, the shank 21,the tamping head 23, the tube 30 and the plug 24, so that it issubstantially equivalent to the mass of the piston 35. By adjusting themasses of these two elements and by forcing them to reciprocate inopposite directions upon the introduction of the compressed air into thechamber 45, both the tool assembly and the piston will move equaldistances, but in opposite directions. While it has been found desirablethat the masses be equal so that the distances moved are also equal, itshould be noted that the equality of mass is not a prerequisite forvibrationless action.

Momentum balance is the critical factor in obtaining such avibration-free mechanism and it is, therefore, contemplated thatdifferent masses can be utilized.

In order to provide a perfectly sealed unit which will not be subject tojamming and other corrosive action occasioned by the materials in theair thrown up by the reciprocating tool. I have provided a bellows-typeseal between the handle and the sleeve 16. This bellows comprises anexpansible bellows member 66 which is secured by means of a ring-likeannulus 61 to a pcripheral groove 62 in the annular flange 12 of thehandle 10. At its opposite end the bellows is secured by means of thering-like projection 63 to the annular groove 64 in the shank 21 of thetool 23. The bellows 66 is preferably made of a resilient material suchas neolite or rubber which is non-porous and which resists abrasion andcorrosion by flying particles. However, it is contemplated that a porousmaterial could be utilized for the bellows 60 so that a filter screen isalso provided. When the rubber non-porous bellows 60 is utilized, it isof course, necessary to provide air flow between the chamber 65 and theatmosphere in order to permit free movement between the handle 10 andthe tool 23. For this purpose I have shown the peripherally spacedapertures 66 which are small enough to act as individual dual filters.If desired, however, larger apertures may be used with a disc-typefilter of conventional design fixed across the openings thereof.

A similar bellows construction is provided at the upper end of the tool.At that end the bellows 67 is secured to the plug 24 and the annularflange 11 by means of the fastening rings 63 and 69 which aresubstantially identical to those utilized with the bellows 60. Apertures70 are also provided to permit air to escape from one side of thebellows 67 to the other.

Besides serving the function of a seal for dirt and other foreignmatter, the bellows 6t and 67 also act as resilient bumper stops againstexcessive movement between the handle 10 and the sleeve 16. Should thehandle 10 be moved excessively relative to the sleeve 16, the bellows 60or 67 will be compressed to a point where it is a compact mass ofresilient rubber which then acts as a bumper to protect the handle 10from impact with the members 21 or 24. It should be noted, however, thatthis bumping feature is not utilized on every stroke of the tamper andit is intended that the handle 11) be positioned by the operator so thatthe bellows 60 and 67 are never compacted to the point where they act asbumpers continually. The strokes of the piston 35 and the tamper 23 aredesigned to be shorter than the combined lengths of the bellows 60 and67, so that the handle may be moved relative to the sleeve 16 duringoperation to place it in an intermediate position such that there is noimpact between the handle 10 and either the member 21 or the plug 24.

In operation, the operator holds the tool in a generally verticallydownward direction in order to obtain a vibrationless, recoillessoperation. One or both hands are used in grasping the hollow handle 10and compressed air is then introduced from a suitable source through thefitting 14. This air passes as above described into the annular chamber20 and then intermittently into the chamber 45 where it expands toreciprocate the piston 35 relative to the member 21 or sleeve 16. Sincethe movements of the piston 35 and the tamper 23 are simul: taneous andin opposite directions, the forces are balanced out and the handle 14)serves merely as a sliding guide for holding the apparatus in an uprightposition.

Since the handle serves no reaction function, no impulses are impartedthrough it to the hand of the operator, thereby permitting the handle 10to remain substantially stationary during operation of the apparatus. Itis, of course noted that the handle remains stationary only so long asit is positioned intermediate the maximum stroke positions of the sleeve16 so that the bellows 60 and 67 do not act as bumpers. Should thebellows act as bumpers, blows will be struck the handle tending to forceit into an intermediate position, after which it will remain stationarywith no impact forces whatever thereon.

As was explained above, the device thus described provides avibrationless action in that no vibration reaches the operator throughthe handle of the mechanism. The apparatus as so far described is alsorecoilless in that when positioned in an upright manner by the handle10, the gravitational efiect on the tamper 23 and the piston 35 is suchas to provide a tamping force in the downward direction. This force,however, is not available when the tamping apparatus is utilized in ahorizontal position or in an inverted position, as for example, in theuse of a riveter or similar apparatus when driving rivets or nails inwalls or overhead structures. In order to overcome this deficiency inthe use of the apparatus in other than a substantially verticallydownward position, I have provided means for adding a constant recoilreaction force to the system.

As may clearly be seen from Figure 5, I have provided an attachmenthousing 75 which may be secured to the annular flange Illa of the handle10. The piston and tamper construction is identical to that alreadydescribed above except that means are provided in the housing 75 foradding a constant force in the direction of intended movement of thetamper 23 to aid or supplant the force of gravity which can be utilizedonly in the vertically downward position of operation.

In providing such a force applying means, I have extended the plug 24 toinclude a longitudinally extending projection 24a thereon. As shown inthe disclosed embodiment, this projection is coaxial with the tube 30and in order to permit the tube 30 to vent to atmosphere as in theconstruction shown in Figure 2, a vent 76 is drilled through theprojection 24a into connection with the recess 34. The projection 24apasses through a bulkhead 77 which is carried by the casing 75 andsecured axially relative thereto by means of thebuttress 78 and thespring retainer 79. A seal 80 is provided between the bulkhead 77 andthe casing 75 to prevent the passage of air from one side of thebulkhead to the other. The projection 24 is slidably carried by thebulkhead and seals 81 prevent the leakage of air along the surface ofthe projection while at the same time insuring a lubricated and,therefore, relatively friction-free bearing surface.

A pistol grip handle 82 of conventional design is provided forsupporting the casing 75. The handle 82 encloses a conventional valvingarrangement which permits control of air from any conventional source ofhigh pressure air or other expansible fluid. The air, after passingthrough the valve in the handle 82 enters an accumulator chamber 83which is located at the top side of the bulkhead 77 as viewed in Figure5. The air is permitted to escape from the chamber 83 to the anularspace 20 between the handle and the sleeve 16 by means of a connectingconduit 84.

It will be appreciated that since the casing 75 completely encloses theplug 24 and the associated end of the sleeve 16, no problem is facedwith respect to preventing dirt and other foreign matter from injuringthe bearing surface 17 between the handle and the sleeve 16. Therefore,instead of using the bellows 67 utilized in Figures 1 and 2, I havesubstituted therefor a resilient bumper 85. This bumper serves the sameresilient shock absorbing function as that described for the bellows 6t)and 67 when in their extreme, compressed position. However, as in thecase of the bellows 6t) and 67, it is intended that the apparatus beoperated by the handle 10 and hence the casing 75, in an intermediateposition relative to the stroke of the piston 16 so that neither thebellows 60 nor the bumper 85 are actually normally utilized as bumpers.

In operation, the apparatus shown in Figure 5 operatesin a mannersubstantially identically to the construction shown in Figures 1 and 2.The internal valving of the tamping mechanism is, of course, identicalto that already described in connection with the structure in Fig-- uresl and 2. However, since there is a constant pres sure in the accumulatorchamber 83, and since the area of the end face 24]) of the projection24a is constant no matter what the position of the piston, a constantforce will be applied tending to force the sleeve 16 away from handle 32as viewed in Figure 5. This force will either supplement, supplant, orovercome the force of gravity which actuates the tool 23, depending uponthe position of the tool, thereby permitting the use of the instrumentin positions other than the vertically downward position.

It will further be apparent that in the operation of the constructionshown in Figure 5, the air which is exhausted from the chamber 45 duringthe exhaust stroke, in which the parts are shown in Figure 5, will movethrough the aperture 44 through the passageway 33, through the port 42into the annular passageway 52 to the port 54 and from there outwardlyalong the passageway 34 through the vent 76 into the chamber 86 and outthrough the aperture 75a in the casing 75 to atmosphere. This in effect,therefore, provides exactly the same exhaust route for the gases asprovided by the construction shown in Figures 1 and 2 and at the sametime permits the addition of a constant biasing force on the sleeve 16tending to maintain it against the work.

It is to be understood, of course, that the accumulator of the chamberconstruction herein shown and utilized in connection with the tamper ofthe present invention could be utilized with other reciprocating toolsprovided that they utilize the isolated handle construction shown inFigures 1 through 5 of the present invention.

While the present invention is described particularly in connection witha camping tool, it is evident that the same principles of operation canbe employed With suitable modification of the hand gripping portion andtool housing to other types of pneumatically operated reciprocatingimpact tools such as rock drills and concrete breakers and the like.

it will be understood that modifications and variations may be effectedwithout departing from the scope of the novel concepts of the presentinvention.

I claim as my invention:

1. A vibrationless pneumatic impact tool comprising an impact member, areactive mass coaxially aligned with said impact member, a handle membercoaxial with said impact member and said reactive mass, said handlehaving means mounting said mass and said impact member for guided freelyslidable movement with respect to each other and said handle andresilient means biasing said mass and impact member against movementaway from each other, said last named means being independent of saidhandle whereby vibrations imposed by said mass and said member are notimposed on said handle.

2. A vibrationless pneumatic impact tool assembly comprising a handlemember, an impact tool arranged for re ciprocation within said handlemember, a reactive mass coaxial with said impact tool and reciprocablymounted within said handle member and mcans for introducing compressedair to said handle and between said impact tool and said reactive massto cause simultaneous relative displacement of said impact tool and saidreacted mass away from each other and resilient means acting betweensaid impact tool and said mass for urging relative displacement of saidimpact tool and said reactive mass toward each other.

3. A vibrationless pneumatic impact tool assembly comprising a handlemember an impact tool having a tool head and a sleeve secured to saidtool head, said impact tool being slidable within said handle member, apiston reciprocal within said sleeve, means for introducing compressedair through said sleeve and between one end of said piston and said toolhead to cause relative displacement of said tool head and said piston inone direction, said piston having means connected therewith to terminatethe flow of compressed air to said tool head after a predeterminedrelative displacement and means for exhaustin g the compressed airbetween said sleeve and said piston after said parts have reached saidpredetermined relative displacement.

4. A vibrationless pneumatic impact tool assembly comprising a hollowhandle member, a tool head and a sleeve secured to said tool head, meansreciprocably mounting said sleeve within said handle member for freereciprocal movement relative thereto and including means directing airbetween said handle and said sleeve against substantially equalbalancing areas at opposite ends of said handle, a piston reciprocalwithin said sleeve, means for introducing compressed air between saidhandle and said sleeve and through said sleeve and between one end ofsaid piston and said tool head to cause relative displace ment of saidtool head and said piston in one direction, said piston being arrangedto terminate the flow of com pressed air to said tool head after apredetermined relative displacement of said tool head and said piston,means for exhausting air between said sleeve and said piston aftertermination of the flow to said tool head, means for terminatingmovement in said one direction, and means causing relative displacementof said piston and said tool head in the opposite direction upontermination of movement of said piston and said tool head in the saidone direction.

5. A vibrationless pneumatic impact tool comprising a handle member, atool subassembly including a tool head and a sleeve secured to said toolhead, said sleeve being reciprocable freely within said handle member, apiston freely reciprocable within said sleeve, a porting tube secured tosaid sleeve and extending coaxially within said sleeve and said piston,means for introducing compressed air through said handle, sleeve andpiston into said porting tube, said porting tube having a port thereinfor directing the air between one end of said piston and said tool headto cause relative displacement of said tool assembly and said piston inone direction, said piston having valve means arranged to terminate theflow of air through said porting tube after a predetermined relativedisplacement of said tube and said piston, and means for exhausting airfrom between said one end of said piston and said tool head after apredetermined relative displacement of said piston and said tool head.

6. A recoilless, vibrationless pneumatic impact tool comprising a hollowhandle member, an impact tool assembly including a tool head, a sleevesecured to said tool head and reciprocable within said hollow handle, apiston reciprocable in said sleeve, said piston being disposed withinsaid sleeve to provide spaced air chambers at op posite ends of saidpiston between said piston ends and said sleeve, means for introducingcompressed air into the air chamber disposed between one end of saidpiston and said tool head to cause relative displacement of said toolassembly and said piston in a first direction, means biasing said pistonand said sleeve in the opposite direction, means actuated by themovement of said piston in said first direction for trapping air in theother of said air chambers during the extreme portion of travel of saidpiston within said sleeve and means for exhausting the air between saidpiston and said tool head upon a predetermined relative displacementbetween said piston and said tool head in said first direction.

7. A vibrationless pneumatic tool comprising a movable tool memberhaving a bore, a piston reciprocable within said bore, a handle memberslidably guiding said tool member and movable independently thereof,means for biasing said piston in a first direction within said bore andmeans for injecting compressed air between said tool member and saidpiston to cause relative motion or" said piston in the other directionin said bore, and means for exhausting said compressed air from betweensaid tool member and said piston upon a predetermined relative motion insaid second direction.

8. A recoilless tool comprising a handle member having air inlet meanstherein, a tool housing guided by said handle member and slidabletherealong, said tool housing having air inlet means communicating withthe air inlet means in said handle member, a piston reciprocablerelative to said housing, said piston having air-directing means thereincommunicating with the air inlet means of said handle member and saidtool housing, to direct air between one end of said piston and an end ofsaid housing, venting means in said housing for venting air from saidhousing during reciprocation of said piston in a first direction andmeans associated with said housing and arranged to close off the airdirecting means in said piston during reciprocation of said piston pasta predetermined position relative to said housing.

9. A constant recoil, vibrationless pneumatic impact tool assemblycomprising a handle member, a reciprocating tool member freely slidablewithin said handle member, piston means mounted for movement relative tosaid tool member and biased into contact with one end of said toolmember by a spring positioned between said piston and the other end ofsaid tool member, means for introducing compressed gas between one endof said tool member and the corresponding end of said piston for movingsaid piston relative to said tool member in opposition to said biasingmeans, valve means associated with said tool member and said piston forterminating how of said compressed gas and for exhausting the gasbetween said piston and said tool member upon the movement of saidpiston relative to said tool member a predetermined distance, andbiasing means associated with said compressed air source for providing aconstant biasing force against said tool member to move said tool memberrelative to said handle in a direction opposite to the movement of saidpiston relative to said tool member.

10. A constant recoil, vibrationless pneumatic impact tool assemblycomprising a handle member, a reciprocating tool member freely slidablewithin said handle member, piston means mounted for movement relative tosaid tool member and biased into contact with one end of said toolmember by a spring positioned between said piston and the other end ofsaid tool member, means for introducing compressed gasbetween one end ofsaid tool member and the corresponding end of said piston for movingsaid piston relative to said tool member in opposition to said biasingmeans, valve means associated with said tool member and'said piston forterminating flow of said compressed gas and for exhausting the gasbetween said piston and said tool member upon the movement of saidpiston relative to said tool member a predetermined distance, andbiasing means for providing a constant biasing force against said toolmember to move said tool member relative to said handle in a directionopposite to the movement of said piston relative to said tool member.

11. A constant recoil, vibrationless pneumatic impact tool comprising ahandle member mounted for guiding a reciprocating tool element formovement independently thereof into engagement with a work piece, areciprocating piston slidable within said tool element and biasedaxially into contact with one end of said tool element by means of aspring positioned between the other end of said tool element and theopposite end of said piston, valve port means in said tool member foralignment with port means in said piston to introduce air from betweensaid handle and said tool element into a space between said one end ofsaid tool element and said piston for moving said piston relative tosaid tool element in a direction opposite to the direction of said bias,means for disturbing the alignment of said ports upon a predeterminedrelative movement between said piston and said tool element to therebycut ofli supply of compressed air, and means for exhausting the airbetween said piston and said tool element upon movement of said pistonpast said predetermined relative position, and biasing means for placinga constant bias on said tool element relative 5 to said handle in thedirection of the work piece.

498,742 Carlinet May 30, 1893 10 10 Johnson Oct. 19, 1897 Robertson Dec.24, 1912 Page May 18, 1926 Shaff Jan. 16, 1940 Butts Dec. 31, 1946Iuilfs Feb. 19, 1952

